import { DestroyRef, effect, inject } from '@angular/core';
import { ActivatedRoute, Router } from '@angular/router';
import { Result } from '@shared/kernel/fp';
import { runSubmit, SUBMIT_FAILED } from '@shared/application/submit';
import { registerPendingSave } from '@shared/application/pending-saves';
import type {
  AanvraagIndienenRequest,
  AanvraagIndienenResponse,
} from '@shared/infrastructure/api-client';
import { AanvraagType } from '@registratie/domain/aanvraag';
import { AanvragenAdapter } from '@registratie/infrastructure/aanvragen.adapter';
import { findConcept, loadConcept } from './find-concept';

/** What a wizard persists per step: the opaque machine snapshot + progress + docs. */
export interface DraftSnapshot {
  draft: unknown;
  stepIndex: number;
  stepCount: number;
  documentIds: string[];
}

export interface DraftSyncDeps {
  type: AanvraagType;
  /** The machine snapshot while it's worth persisting; null when not (pristine/done). */
  snapshot: () => DraftSnapshot | null;
  /** Seed the machine from a resumed draft. Called at most once, on init, and ONLY
      with a real draft on a still-pristine machine — see `applyResume`. */
  onResume: (draft: unknown) => void;
  /** Draft-sync only runs in the real app — false in Storybook/tests (explicit seed). */
  enabled: () => boolean;
}

const DEBOUNCE_MS = 600; // ponytail: fixed debounce; tune if the sync feels laggy/chatty.

/**
 * The effectful glue that replaces per-wizard sessionStorage with a backend-owned
 * Concept (PRD 0001, phase D). Instantiated in a field initializer (like
 * `createStore`/`createUploadController`). Responsibilities:
 *
 *  - resume: a `?aanvraag=<id>` link wins; otherwise resume the ONE existing Concept of
 *    this type (at most one per type), seeding the machine from its saved draft;
 *  - create-on-first-progress: when no Concept exists, one is created lazily the first
 *    time the wizard reports a non-null snapshot, and its id is stamped into the URL;
 *  - debounced draft sync on every subsequent change.
 *
 * Inert without a Router (stories) or when `enabled()` is false — no network, no resume.
 */
export function createDraftSync(deps: DraftSyncDeps) {
  const adapter = inject(AanvragenAdapter);
  const router = inject(Router, { optional: true });
  const route = inject(ActivatedRoute, { optional: true });
  const active = () => deps.enabled() && !!router && !!route;

  let id: string | undefined;
  let ensuring: Promise<string> | undefined; // in-flight create, so we never create twice
  let timer: ReturnType<typeof setTimeout> | undefined;
  // Resolves once resume() has decided whether a Concept of this type already exists;
  // gates ensureId so a fast typist can't create a duplicate before that lookup lands.
  let resumeGate: Promise<unknown> = Promise.resolve();

  const ensureId = async (): Promise<string> => {
    await resumeGate;
    if (id) return id;
    ensuring ??= adapter
      .create(deps.type)
      // One Concept per type is server-enforced. Within a tab the resumeGate
      // already prevents a second create, but a cross-tab/stale race can still hit the
      // server's guard (409) — recover by adopting the existing Concept instead of
      // erroring. Only recover when one actually exists; otherwise surface the failure.
      .catch(async (e) => {
        const existing = await findConcept(adapter, deps.type);
        if (existing) return existing;
        throw e;
      })
      .then((newId) => {
        id = newId;
        // Stamp the id into the URL (no navigation) so a reload resumes this Concept.
        void router!.navigate([], {
          relativeTo: route!,
          queryParams: { aanvraag: newId },
          queryParamsHandling: 'merge',
          replaceUrl: true,
        });
        return newId;
      });
    return ensuring;
  };

  // Apply a resumed draft only when it's safe to: a late lookup must never clobber
  // progress the user already made while it was in flight, and "start fresh" needs no
  // dispatch (the machine already starts fresh). snapshot() is non-null once the user
  // has real progress.
  const applyResume = (draft: unknown | null) => {
    if (draft == null || deps.snapshot() != null) return;
    deps.onResume(draft);
  };

  const flush = async () => {
    const snap = deps.snapshot();
    if (!snap) return;
    const theId = await ensureId();
    await adapter.syncDraft(theId, {
      draft: snap.draft,
      stepIndex: snap.stepIndex,
      stepCount: snap.stepCount,
      documentIds: snap.documentIds,
    });
  };

  // One effect watches the snapshot; each change resets a debounce timer. The timer's
  // callback only does network I/O (never dispatch), so it can't livelock the store.
  effect(() => {
    if (!active()) return;
    const snap = deps.snapshot(); // tracked: fires on every machine change
    if (!snap) return;
    if (timer) clearTimeout(timer);
    // Null the handle when it fires so `hasPendingSave()` reflects "a write is still owed".
    timer = setTimeout(() => {
      timer = undefined;
      void flush();
    }, DEBOUNCE_MS);
  });

  inject(DestroyRef).onDestroy(() => timer && clearTimeout(timer));

  // Flush a pending debounced draft write before an in-app route change / unload (see
  // pending-saves.ts). onDestroy above only cancels the timer — this actually persists it.
  const hasPendingSave = () => timer !== undefined;
  const flushPending = async () => {
    if (timer === undefined) return;
    clearTimeout(timer);
    timer = undefined;
    await flush();
  };
  registerPendingSave({ hasPendingSave, flushPending });

  // Attach to a specific Concept id and seed the machine from its draft. A non-Concept
  // (submitted/gone) id is treated as fresh so it can't reopen as an editable draft.
  const load = (linked: string): Promise<void> => {
    id = linked;
    return loadConcept(adapter, linked).then((result) => {
      if (result.tag === 'not-concept') {
        id = undefined;
        applyResume(null);
        return;
      }
      applyResume(result.draft);
    });
  };

  return {
    /** True while a debounced draft write is still pending (PendingSave). */
    hasPendingSave,
    /** Flush the pending draft write now and await it; no-op when nothing is pending. */
    flushPending,

    /** Resolve the initial state: a `?aanvraag` link wins; else resume this type's
        existing Concept; else start fresh (a Concept is created on first progress). */
    async resume() {
      let release!: () => void;
      resumeGate = new Promise<void>((r) => (release = r));
      try {
        if (!active()) {
          applyResume(null);
          return;
        }
        const linked = route!.snapshot.queryParamMap.get('aanvraag');
        if (linked) {
          await load(linked);
          return;
        }
        const existing = await findConcept(adapter, deps.type);
        if (existing) {
          await load(existing);
          // Stamp the id into the URL so a reload resumes the same Concept.
          void router!.navigate([], {
            relativeTo: route!,
            queryParams: { aanvraag: existing },
            queryParamsHandling: 'merge',
            replaceUrl: true,
          });
          return;
        }
        applyResume(null);
      } finally {
        release();
      }
    },

    /** Submit through the aanvraag lifecycle: ensure the Concept exists, then
        `POST /applications/{id}/submit` (server sets autoApprovable + transitions).
        Folded into a Result like the old submit-* commands. */
    submit(body: AanvraagIndienenRequest): Promise<Result<string, AanvraagIndienenResponse>> {
      return runSubmit(async () => adapter.submit(await ensureId(), body), SUBMIT_FAILED);
    },

    /** Restart: discard the current in-progress Concept (delete it) and detach, so a
        fresh one is created on next progress. Keeps the one-per-type invariant. A
        submitted id can't be deleted (409, caught) — that submission correctly remains,
        and detaching still lets the user start a new Concept. */
    reset() {
      if (id) {
        void adapter.cancel(id).catch(() => {}); // Concept → deleted; submitted → 409, kept
        id = undefined;
        ensuring = undefined;
      }
      if (active())
        void router!.navigate([], {
          relativeTo: route!,
          queryParams: { aanvraag: null },
          queryParamsHandling: 'merge',
          replaceUrl: true,
        });
    },
  };
}